While I do sympathize, I wonder how the actual figures work out for aircraft regularly flown IFR.
I taught someone for their instrument rating about 4 years ago in a non-GPS equipped aircraft. Since then, in the dozens of owners' airplanes I've flown and taught in, only one did not have a WAAS GPS - and that one was an early G1000-equipped aircraft, so not exactly an "old school" aircraft - and that one non-GPS aircraft now does have a 430W. All of these were normal, light GA airplanes, single and twin-engine pistons. Many were 60's and 70's vintage.
Perhaps my experience is not typical, but at least among my client list, the number of non-WAAS aircraft is vanishingly tiny.